1. Field of the Invention
This invention relates to a measuring device for measuring the configuration of an object, and more particularly, to a measuring device with a stylus movable along an object so as to measure its configuration.
2. Prior Art
It is well known in the prior art to use a measuring device for measuring the configuration of an object. Such a device has a stylus movable along the object as is generally shown in U.S. Pat. No. 3,319,341. The prior art device has a stylus at one end of a rotatable arm with a weight mounted at the other end of the arm such that the weight keeps the balance so as to maintain the stylus in touching relationship with the object as the stylus moves smooth relative to the object. Thus, the prior art device measures the configuration of the object through the movement of the stylus.
Referring to FIG. 1, there is shown the basic structure of a stylus arm of the prior art. The arm 201 is rotatably held by a cross spring 202 midway along arm 201. Arm 201 is further provided with a stylus 203 at one end and an adjustable weight 204 at the other end. In this device, usually the center of the gravity G1 on the stylus side which is represented by weight W1 of the arm 201 from the fulcrum 0 to the end and the center of the gravity G2 on the weight side represented by the weight W2 of the arm 201 from the fulcrum 0 to the other end are both higher than the horizontal line P which runs across fulcrum 0. In other words, the lines connected between the fulcrum 0 and the center of gravity G1 and the other center of gravity G2 do not form a straight line; rather, form a V-shape line. It has been found that such device results in undesirable requirements in a force necessary to be used on a stylus when the device is used.
Referring now to FIGS. 2(A) and 2(B) one can see in illustration of the drawback of such prior art device in terms of the difference in the force on the stylus. To simplify this explanation, weights are loaded at the center of gravity G1 and G2 and are assumed to be the same. These weights are referred to in the drawings in FIG. 2 as W and the distance from the fulcrum 0 to the center of gravity G1 and to the center of gravity G2 are assumed to be the same and indicated as length l.
Shown in FIG. 2(A), when the arm is kept horizontal, the angle formed by the line between the center of gravity G1 and the fulcrum 0 and the horizontal line P, and the angle formed by the line between the center of gravity G2 and the fulcrum 0 is indicated by .theta.; further, the moment about the fulcrum 0 at the center of gravity G1 and G2 when balance can be represented by the formula W.multidot.l cos .theta..
As shown in FIG. 2(B), when the left side of the arm is disposed downward, angle formed by the line between the center of gravity G1 and the fulcrum 0, and the horizontal line P is .theta.. The angle formed by the lines between the center of gravity G2 and the fulcrum 0, and the horizontal line P is .theta..sub.2. The moment at the center of gravity G1 is therefore represented by the formula W.multidot.l cos .theta..sub.1, and the moment at the center of gravity G2 is represented by the formula W.multidot.l cos .theta..sub.2. Since the angles .theta., .theta..sub.1, and .theta..sub.2 have a relation to one another as follows: .theta..sub.1 &lt;.theta.&lt;.theta..sub.2, there exists a relationship as follows: l cos .theta..sub.1 &gt;l cos .theta.&gt;l cos .theta..sub.2. Therefore, the moment the center of graviry G1 and G2 have a relationship represented as follows: W.multidot.l cos .theta..sub.1 &gt;W.multidot.l cos .theta..sub.2. As a result, the imbalance cause creates a counter-clockwise moment. This means that the stylus receives an additional measuring force which has been found to be a significant disadvantage in connection with measuring the configuration of an object.
In the above explanation although it is assumed that the moment at the center of gravity G1 is the same as the moment at the center of gravity G2, it has been found that in actual device, the moment at the center of gravity G1 is designed so as to be slightly greater than the other i.e., G2 such that the stylus receives some measuring force. However, there are still shortcomings associated with such a stylus. Further, in such a case the device can lean on the other direction when the measuring force that the stylus receives is decreased. In either situation, the measuring force is not stable. This has been found to be true regardless of the angles formed and the distance between the fulcrum 0 and the center of gravity G1 and G2 or the position of the centers of gravity G1 and G2 either being above or below the fulcrum 0.
In summary, in the prior art device no attention was paid to the relationship between the fulcrum 0 and the centers of gravity G1 and G2. Therefore, it has been found that the measuring thus obtained includes somewhat inaccurate information unless the device is used so as to keep the device in a strictly horizontal position. This can substantially limit the use of device and thus represents a shortcoming.
It is therefore, an object of this invention to provide a measuring device which keeps the constant force on the stylus even when the device is being used such that the arm is bending forward and backward.